LESSON 4 - ACTIVITY 1 - THE EFFECTS OF AIR TEMPERATURE ON AIR PRESSURE
Objectives
Materials
Background Information
Key Questions
Vocabulary
Procedure
Evaluation
Objectives
- Define air pressure.
- Describe what happens when air is cooled or heated.
- Explain how the temperature of the air affects air pressure.
Materials
- hotplate
- pan
- 2 beakers
- water
- 2 tea bags or food coloring
- Dry cleaner plastic film bags (select a bag with the thinnest possible plastic and have several on hand. You may have to experiment with bags of different thickness.)
- Several small paper clips
- Cellophane tape
- Hair Dryer
- several empty soda cans
- tongs
- gloves
- bowl of very cold water
- thin long stick (about 1 inch wide, 36 inches long, 1/4 inch thick)
- sheet of newspaper
Background Information
Then Earth's surface is heated by solar radiation. The heat from the ground is transferred into the air via conduction. When air receives a certain amount of heat from the ground, it will expand, become less dense and be pushed up by buoyancy. Cooler, heavier air will sink under it, which warms it, causing it to expand and rise. This warm air that is rising will cool down when it hits higher, colder areas of the atmosphere and will become more dense. This cool air can not sink through the warm air that is rising beneath it, so it begins to move sideways before it sinks. Once it sinks to the surface again, it warms back up, and gets drawn back up into the original column of rising air. This movement of air, or convection currents, create wind, air thermals, tornados and thunderstorms. On a grander scale, they produce the global movement of the atmosphere.
A convection cell is an area of air that has rising & falling air.
This is how hot air balloons work. Air in the balloon is heated by a large burner which causes the balloon to expand and the heated air causes the balloon to rise.
Convection Image NASA
Key Questions
- What happens to air when it is cooled or heated?
- How does air temperature affect air pressure?
Vocabulary
- air pressure
- barometer
Procedure
Introduce this activity by asking students if they have ever made tea. Ask them if it is easier to make tea with hot water or cold water. Explain to the class that the water in this activity is being used to represent the air in our atmosphere. The water molecules will behave in the same manner as air molecules when heated and when cooled. If you heat water, the molecules begin to move. The more they are heated, the faster they move.
Materials:
hotplate
pan
2 beakers
cold water
boiling water
tea bags or food coloring
Procedure: Heat water to boiling in the pan on the hotplate. Fill one beaker 3/4 full with boiling water and fill the other beaker with cold water. Place a tea bag or a few drops of food coloring in each beaker. Point out that the students should observe the movement of the tea or food color.
Discussion: Ask your students how this experiment relates to air molecules. Air molecules move fast and are far apart when heated. They slow down and are closer together when cooled. The teabag or food coloring in the heated water should have diffused faster than the cold water.
2. Demonstrate what happens when air is heated by making a hot air balloon.
Materials:
Thin plastic bags (a produce bag or dry cleaner bag)
paper clips
clear tape
hair dryer
Procedure: Seal up any tears in the bag with the clear tape. Add paper clips to the open end to keep the bag upright. You'll have to test this to see how many you'll need. Power up the hair dryer and place it under the open end of the bag. The goal is to catch the hot air from the hair dryer inside of the plastic bag. Be careful not to melt the bag. When the plastic bag is filled with hot air, let go of it. If it doesn't rise quickly, fill it with hot air again. If it won't go straight up, add more paper clips to the open end.
Discussion: Ask your students why the hot air balloon rose. Placing the dry cleaner bag over the heat source captures the hot air and forces out the cooler air in the bag. The bag becomes a mass of low-density, warm air which floats upward in the more dense, cooler air surrounding it.
3. Air pressure, or atmospheric pressure, is the weight of air pushing down on us. At sea level, the atmosphere exerts a force of 14.7 pounds per square inch. We have air pressure and water pressure inside of us that pushes up and out, against the air pressure on top of us.
Perform the following experiment to demonstrate air pressure.
Materials:
hotplate
several empty soda cans
tongs
gloves
bowl of very cold water
Procedure: Make sure the soda cans are clean. Prepare the bowl of cold water, the colder the better. Put water in the soda can, just enough to cover the bottom of the can. Place the soda can on the hotplate. Turn on the hot plate and heat the can until the water begins to boil. Continue heating the can for one minute. Using the tongs, grasp the can near the bottom in such a way that your palm is facing up. In one swift motion, lift the can, invert it and plunge it top down into the cold water. The can will implode.
Here's what happened. Before you heated it, the can was filled with water and air. When you boiled the water, it changed from a liquid to a gas. This gas is called water vapor. The water vapor pushed the air out of the can back out into the atmosphere. When you turned the can upside down and placed in the cold water, the water vapor in the can condensed and turned back into the water. Water molecules in a liquid state are spaced much closer together than molecules are in a gas state. All of the water vapor that filled up the inside of the can was transformed into only a drop or two of liquid when it was cooled, which takes up much less space. This small amount of water does not exert very much pressure on the inside walls of the can, so the pressure of the air pushing from the outside of the can is great enough to crush it.
Discussion: Discuss with your students what they observed.
4. Air pressure, or atmospheric pressure, is the weight of air pushing down on us. At sea level, the atmosphere exerts a force of 14.7 pounds per square inch. We have air pressure and water pressure inside of us that pushes up and out, against the air pressure on top of us.
Perform the following experiment to demonstrate air pressure.
materials:
long thin stick (about 1 inch wide, 36 inches long, 1/4 inch thick)
full sheet of newspaper.
Procedure: Place the long thin stick on the edge of a desk, with about 4 inches of the stick hanging off of the edge of the desk. Place the full sheet of newspaper over the stick. Do not allow the newspaper to hang off of the edge of the desk and make sure the paper is flat on the desk and the stick with no pockets of air under the paper. Strike the stick with a quick, sharp blow with the palm of your hand. The paper will not move.
Here's what happened. Air exerts a force of 14.7 pounds per square inch. Imagine a column of air resting on the paper that extends to the edges of the atmosphere. If we calculate the area of the newspaper, approximately 20 x 30 inches, we get 600 square inches. Now, multiply that by 14.7 and you get 8,820 pounds! It's no wonder the paper didn't move.
5. Have your students access the internet to read about the effects of the temperature of the Gulf Stream on weather, global warming, and the greenhouse effect. Useful links are included in the student's pages.
Begin a discussion about how the ocean affects the weather. Ocean currents move heat from the tropics to the poles. Sea-surface temperatures determine the amount of heat that is transferred between the ocean and the atmosphere and the amount of CO2 that can be absorbed from the atmosphere. Greenhouse gases are made up of water vapor, which is responsible for 36-70% of Earth's greenhouse effect; carbon dioxide, which causes between 9-26%; and ozone, which causes between 3-7%.
6. Have your students access the internet to gather temperature data, barometric pressure readings and other relevant weather data for five different cities in the US. Your students will chart the data they have collected. Use the following chart headings: Location/Region, Barometric Pressure, Temperature, Weather Conditions. Based on what they have learned so far, have your students make weather predictions based on the data they have collected. Have them write a summary of their understanding of the properties of air based on temperature (is the air light or heavy based on the temperature) and molecule activity (will the molecules be close together or far apart based on the temperature).
7. Discuss the charts. What predictions can be made about the weather based on air temperature and barometric pressure?
Evaluation
Students will be able to chart data collected regarding air pressure and temperature.
Students will record in their journal a summary of what they have learned about the affects of air temperature on air pressure.
